The invention relates to a method for monitoring the condition of a grinder stone of a pulp grinder.
The invention also relates to a measuring arrangement for monitoring the condition of a grinder stone of a pulp grinder.
In pulp grinders, fiber is removed from wood by pressing wooden material, such as blocks of wood, wood chips etc., against the surface of a grinder stone rotating in its longitudinal direction and simultaneously spraying water onto the grinding surface of the grinder stone, whereby, as a result of the grinding effect of the grinder stone and the softening effect of the water, wood fibers are removed from the blocks and form a pulp suspension with the water. The abrasiveness and grinding properties of the grinder stone depend on the surface pattern and grain of the grinder stone. The abrasiveness and grinding properties of the grinder stone change during the grinding, as the grinding surface of the grinder stone wears. As the surface of the grinder stone wears, the properties of fibers produced during the grinding and the properties of the pulp suspension change and thus the usability of the pulp in paper manufacture, for instance, and the properties of the manufactured paper vary.
One reason why the grinding surface of a grinder stone wears are local temperature differences on the grinding surface of the grinder stone, which increase the wear of the grinding surface of the grinder stone by breaking the grinding surface due to local thermal expansions and thus shorten the service life of the grinder stone surface. This problem is familiar to all grinder stones but its consequences are particularly emphasized in connection with grinder stones which have a grinding surface made of ceramics or a ceramic mixture. Local temperature differences can be caused, for instance, so that the grinder stone becomes locally blunt during the normal grinding or if the grinder stone surface is cooled insufficiently. These, in turn, can be caused, for instance, because the grinder stone becomes naturally blunt, jet nozzles spraying water onto the grinding surface of the grinder stone become blocked, a foreign object arrives on the grinding surface or because of the ‘vertical chamber’ of the grinder, in which the wood is ground endwise.